Silicon-on-sapphire (SOS) plays an important role as material especially suited for radiation-hard integrated circuits. The SOS technology has also been considered as a potential contributor to high performance very large scale integrated (VLSI) and very high scale integrated (VHSI) circuit applications. Recent work on SOS devices has clearly demonstrated a direct relationship between the crystalline perfection of SOS films and device parameters. It has also been shown that crystalline imperfections have a detrimental effect on electronic properties of SOS films, such as excess carrier lifetime, trapping centers, degree of amorphization and microscopic electrical inhomogeneities.
The pace of the optimization of the properties of materials in the heteroepitaxial silicon technology is closely related to the ability to characterize the quality of the deposits. The entire thickness of the film can be observed by cross-section transmission microscopy, but this method is laborious and time consuming, and therefore cannot serve as a rapid feed-back for material optimization efforts. UV reflectometry now serves as a rapid method to characterize the crystalline quality of the heteroepitaxial silicon surface most remote from the silicon/sapphire interface. See U.S. Pat. Nos. 4,352,016 and 4,352,017 issued on Sept. 22, 1982 to M. L. Duffy, et al. for a description of the use of U.V. reflectivity for determining the quality of silicon layers. No method is currently available, however, for the characterization of the crystalline nature of the silicon near or at the silicon/sapphire interface. Specific aspects of device performance (for instance, leakage current) are associated with the properties of the silicon near the sapphire interface. Such information is quite useful to the art.